WO2020249137A1

WO2020249137A1 - Targeted formation method for lithium-ion battery, and lithium-ion battery

Info

Publication number: WO2020249137A1
Application number: PCT/CN2020/103832
Authority: WO
Inventors: 王绥军; 黎可; 孙召琴; 穆居易; 胡晨; 金翼; 尹秀娟; 邢昱
Original assignee: 中国电力科学研究院有限公司; 国网安徽省电力有限公司电力科学研究院; 国家电网有限公司
Priority date: 2019-06-11
Filing date: 2020-07-23
Publication date: 2020-12-17
Also published as: CN110380146B; CN110380146A

Abstract

Provided in the present application are a targeted formation method for a lithium-ion battery, and a lithium-ion battery, the method comprising the following steps: pre-determining an electric potential range for gas generation in a lithium-ion battery in a formation process; within the electric potential range for gas generation and below a preset temperature, using a current of no greater than 0.2 C to charge the lithium-ion battery; and after resting for a preset time, discharging the lithium-ion battery with a current of no greater than 0.5 C to a preset electric potential.

Description

Target formation method of lithium ion battery and lithium ion battery

This application claims the priority of the Chinese patent application filed with the Chinese Patent Office with application number 201910502394.3 on June 11, 2019. The entire content of the above application is incorporated into this application by reference.

Technical field

This application relates to the technical field of lithium ion batteries, for example, to a targeted formation method of lithium ion batteries and lithium ion batteries.

Background technique

In recent years, new energy vehicles and distributed energy have developed rapidly, and the energy storage industry has also ushered in a period of rapid growth. Electrochemical batteries represented by lithium-ion batteries are widely used in electric vehicles and energy storage markets due to their superior characteristics such as high energy density, no memory effect, and no pollution. Electrochemical energy storage also puts forward higher requirements on battery safety, cost and consistency. Lithium-ion batteries have become the mainstream development direction in the field of electrochemical energy storage due to their excellent electrochemical performance. The requirements of energy storage conditions for lithium-ion batteries can be summarized as long life, high safety and low cost. In the process of preparing lithium-ion batteries, formation is an important process. Formation is the first charging of the battery after liquid injection and storage to form a solid electrolyte interface membrane (SEI). The SEI film formed by different chemical conversion processes is different. The shape of the SEI film directly affects the overall performance of the single cell, especially the cycle performance of the battery. The traditional low-current precharge method helps to form a stable SEI film. However, long-term low-current or high cut-off voltage charging will cause the impedance of the formed SEI film to increase, thereby affecting the cycle performance and rate performance of the battery. At the same time, low-current charging requires a long time to form a process, which will result in low production efficiency and increase the production cost of lithium-ion batteries. In addition, the research found that the formation voltage will also affect the formation of the battery SEI film, because the formation of a lithium-ion battery is a first activation process. As the charging progresses, the internal voltage of the battery rises and is accompanied by the generation of gas. If the gas production rate is higher than the exhaust rate of the liquid injection hole, the gas will accumulate between the separators inside the battery, which will affect the formation of the SEI film on the negative electrode surface.

It can be seen that the formation of lithium-ion batteries is an important process in the production process, and the quality of formation directly affects the performance of the battery. The formation process includes electrolyte infiltration, battery interface activation, battery side reactions and SEI film formation. The formation method will be through the growth of the SEI film, which has a great impact on the battery performance. Although the traditional low current formation process can obtain a better positive and negative electrode interface, its process is complicated, and it takes a long time and has a high production cost. At present, high-temperature, high-pressure and high-current chemical formation has attracted wide attention from researchers because it can effectively shorten the formation time and improve production efficiency. Applying a certain pressure to the battery is conducive to shortening the diffusion distance of lithium ions, and at the same time, it can ensure that the positive and negative interfaces of the battery are flat and evenly contacted, which is conducive to the uniform distribution of electrons; and in the formation process, applying high temperature can reduce the electrolyte Viscosity accelerates the diffusion of ions and ensures that electrons and ions are quickly combined under high current. However, if the surface pressure of the cell is too small, the contact of the pole pieces will not be uniform and sufficient, which is the same as the traditional formation method; when the surface pressure of the cell is too high, the electrolyte on the electrode surface will be squeezed out and the ion concentration will decrease, which is not conducive to SEI Film formation; for the formation temperature, when the formation temperature is too low, due to the large formation current used, the ion velocity cannot match the speed of the electrons, which has an impact on the formation of the SEI film; when the formation temperature is too high, it affects the electrolyte and materials And later performance has an impact.

Different formation methods produce different SEI films with different performances. Different SEI films have a great impact on battery performance, including both electrical performance and safety. The dense and smooth SEI film affects lithium dendrites. The growth has a better inhibitory effect. Lithium dendrites refer to the dendritic metal lithium element formed by the reduction of lithium ions when a lithium battery using a liquid electrolyte is charged. Lithium dendrites are the main cause of safety problems. During the charging and discharging process, metal lithium will deposit unevenly on the electrode surface, forming lithium dendrites, and their continuous growth may pierce the diaphragm and cause internal short circuits in the battery. , Leading to serious security problems. After studying the growth mechanism of lithium dendrites, it is found that improving the surface morphology of the negative electrode of lithium-ion batteries, interfering with or inhibiting the directional deposition of lithium ions on the surface of the negative electrode to form lithium dendrites is a long-term effective method to inhibit lithium dendrites. By optimizing the formation method, a dense and smooth SEI film is produced on the surface of the negative electrode of the lithium ion battery, which interferes with the deposition of lithium on the surface of the SEI film, which is a good method to inhibit the growth of lithium dendrites and improve the safety performance of the battery.

In summary, the formation method through the growth of the SEI film has a greater impact on the electrochemical performance and safety performance of lithium-ion batteries, and plays an important role in battery production and applications. However, at present, both long-term low-current formation and high-voltage, high-temperature, high-current formation methods have problems such as complex process and high cost.

Summary of the invention

The present application provides a lithium ion battery targeted formation method and a lithium ion battery to solve the problem of long time required for the formation method and poor formation effect.

This application proposes a lithium-ion battery targeted formation method, which includes the following steps: predetermining the potential interval of the gas produced by the lithium-ion battery in the formation process; within the determined potential interval of gas production and at a preset temperature A current of 0.2C is used to charge the lithium ion battery; after standing for a preset time, the lithium ion battery is discharged to a preset potential with a current of not less than 0.5C.

This application also proposes a lithium ion battery in which the above-mentioned lithium ion battery targeted formation method is used for chemical transformation.

Description of the drawings

FIG. 1 is a flowchart of a method for targeted formation of a lithium ion battery provided by an embodiment of the present invention;

2 is a schematic diagram of potential changes in the gas generation stage during the charging and discharging process in the lithium ion battery targeted formation method provided by an embodiment of the invention;

Fig. 3a is a transmission electron microscope (TEM) image of the negative electrode surface without SEI film before formation of a lithium ion battery;

FIG. 3b is a TEM image of the negative electrode surface of the SEI film generated by the targeted formation method of the lithium ion battery provided by the present application;

Fig. 3c is a TEM image of the negative electrode surface of the SEI film produced by the related lithium ion battery formation method.

Detailed ways

Hereinafter, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other if there is no conflict. Hereinafter, the present application will be described in detail with reference to the drawings and in conjunction with embodiments.

Referring to FIG. 1, the targeted formation method of lithium ion battery provided by an embodiment of the present invention includes the following steps:

Step S1: Predetermine the potential interval of the gas produced by the lithium ion battery in the formation process.

Due to the formation of lithium-ion batteries, side reactions will occur in a specific potential range, producing gases such as H2, CH4, CO2, and C2H6. At the same time, it is accompanied by the production of SEI film; but not the entire charging or discharging process produces gas and SEI The growth of the film, therefore, accurately grasp the potential range of lithium-ion battery gas production and SEI film growth, and effectively set the relevant potential range for charge and discharge, which can effectively improve the efficiency of the formation while ensuring the formation effect.

In specific implementation, a charge and discharge cycle of the lithium ion battery may be performed in advance with a current not greater than 0.1C, and the potential interval of gas generation during the charge and discharge process of the lithium ion battery is recorded. In this embodiment, the lithium-ion battery can be charged and discharged in advance at a charging current of 0.1C, and gas chromatography is used to record the gas generation during the charging and discharging process of the lithium-ion battery in situ to determine the gas generation potential Interval. As shown in Figure 2, taking the lithium iron phosphate battery as an example, in the potential range of 3.38-3.48V, the lithium iron phosphate battery generates gas during the formation process.

In step S2, in the gas production potential interval determined in the step 1, a current not greater than 0.2C is used to charge the lithium ion battery at a preset temperature.

Since the gas production reaction is more sensitive to temperature, the temperature can be used to control the gas production rate within a reasonable range. In order to ensure that the gas generating reaction occurs at a normal rate, the temperature cannot be too low; in order to avoid the rapid occurrence of the gas generating reaction, the surface of the SEI film is not smooth, the temperature cannot exceed 45°C. Optionally, the preset temperature is 25-45°C, and in this embodiment, the preset temperature is 30°C.

In specific implementation, after determining the gas generation potential interval, the lithium ion battery can be charged with a relatively small current, for example, a current of 0.1C, 0.15C or 0.2C.

In this embodiment, in the potential interval where there is no gas generation, charging with a current of not less than 0.5C can accelerate the formation rate without affecting the generation of the SEI film.

Step S3: After standing for a preset time, discharge the lithium ion battery to a preset potential with a current of not less than 0.5C.

Optionally, the standing time is 5-60 minutes, and in this embodiment, the standing time is 10 minutes. Among them, the preset potential is the termination potential of discharge, which needs to be determined according to the battery type. For example, the termination potential of lithium iron phosphate is within 2.6-2.9V, and the termination potential of lithium titanate is within 1.4-1.6V.

Obviously, it can be concluded from the above that the targeted formation method for lithium-ion batteries provided in this embodiment determines the potential interval of gas generated during the formation of the lithium-ion battery, and conducts the lithium-ion battery with a smaller current in the potential interval of gas generation. Charging, charging the lithium-ion battery with a larger current in other potential ranges; further controlling the formation temperature of the gas generating range is conducive to the formation of a dense and smooth SEI film on the negative electrode surface of the battery, which significantly improves the battery performance while greatly improving In order to improve the formation efficiency of the battery, the method is simple and easy to implement, and can be quickly applied to production.

A lithium ion battery adopts the above-mentioned lithium ion battery targeted formation method for chemical conversion treatment.

The lithium-ion battery of the present application adopts the above-mentioned lithium-ion battery formation method for chemical treatment, so that the lithium-ion battery provided by the present application has better cycle performance and safety.

The following uses lithium iron phosphate battery as a specific example to describe this application in detail:

The first step is to determine the potential interval of gas production is 3.38-3.48V;

The second step, as shown in Figure 2, the targeted formation process steps include:

(1) Charge the lithium iron phosphate battery to 3.38V with a constant current of 0.5C;

(2) Charge the lithium iron phosphate battery from 3.38V to 3.48V at a constant current of 0.1C at 25-45°C;

(3) Charge the lithium iron phosphate battery from 3.48V to 3.75V with a constant current of 0.5C;

(4) Let stand for 10 minutes;

(5) Discharge the lithium iron phosphate battery from 3.75V to 2.8V at a constant current of 0.5C.

3a-3c, it can be seen that the surface of the SEI film of the lithium iron phosphate battery obtained by the targeted formation method provided by this application is smooth and compact, as shown in Figure 3b; while the related formation method not only takes a long time, but also the surface of the SEI film Rough, not dense, as shown in Figure 3c. Therefore, the battery formed by the present application has good electrochemical performance, and the electrode surface also has a smooth and dense SEI film, which can effectively inhibit the growth of lithium dendrites.

Claims

A targeted formation method for lithium ion batteries includes the following steps:

Predetermine the potential interval of the gas produced by the lithium ion battery during the formation process;

Charging the lithium ion battery with a current not greater than 0.2C in the determined potential interval for gas production and at a preset temperature;

After standing for a preset time, the lithium ion battery is discharged to a preset potential with a current of not less than 0.5C.
The method for targeted formation of a lithium ion battery according to claim 1, wherein the predetermined potential interval for gas generation in the formation process of the lithium ion battery comprises:

A charge and discharge cycle of the lithium ion battery is performed in advance with a current not greater than 0.1C, and the potential interval of gas generation during the charge and discharge of the lithium ion battery is recorded.
2. The lithium ion battery targeted formation method according to claim 2, wherein gas chromatography is used to record the gas generation during the charging and discharging process of the lithium ion battery in situ to determine the gas generation potential during the charging and discharging process of the lithium ion battery Interval.
The method for targeted formation of lithium ion batteries according to claim 1, 2 or 3, wherein the potential range of the gas generation of the lithium ion battery is 3.38-3.48V.
The method for targeted formation of lithium-ion batteries according to claim 1, wherein charging the lithium-ion battery with a current of not more than 0.2C comprises: charging the lithium-ion battery with a current of 0.1C.
The lithium ion battery targeted formation method according to claim 1 or 5, wherein the preset temperature is in the range of 25-45°C.
The method for targeted formation of lithium ion batteries according to claim 6, wherein the preset temperature is 30°C.
The method for targeted formation of lithium-ion batteries according to claim 1, wherein charging the lithium-ion battery with a current of not more than 0.2C further comprises: using a current of not less than 0.5C in a potential interval where no gas is generated. The lithium ion battery is charged.
The method for targeted formation of a lithium ion battery according to claim 1, wherein the range of the preset time of standing is 5-60 minutes.
The method for targeted formation of a lithium ion battery according to claim 9, wherein the preset time of standing is 10 minutes.
A lithium ion battery, wherein the lithium ion battery is chemically transformed through the lithium ion battery targeted chemical transformation method according to any one of claims 1 to 10.